Thiolcarbamates are an important class of industrial chemicals which can be used as intermediates for synthesis of other chemicals. Many thiolcarbamates have also been used as herbicides, insecticides, and fungicides or bacteriocides for inhibiting the growth of microorganisms.
A thiolcarbamate such as, for example, S-ethyldipropylthiolcarbamate, has been prepared by reacting a secondary amine such as dipropylamine with phosgene to produce a carbamoyl chloride. The carbamoyl chloride is in turn reacted with a thiolate such as sodium alkylmercaptide to produce the corresponding thiolcarbamate. However, using phosgene is generally a safety concern because of its toxicity. Additionally, when phosgene is used, two, three if the alkyl mercaptide is made from an alkylhalide, mole equivalents of halide waste are produced as by-products.
A thiolcarbamate has also been prepared by reacting two mole equivalents of a secondary amine with carbonyl sulfide, in the presence of an aromatic solvent such as, for example, toluene to form a thiolcarbamic acid which further reacts with a hydrocarbyl chloride such as, for example, benzyl chloride to produce a thiolcarbamate. Carbonyl sulfide is generally much easier to handle and safer to use than phosgene. Additionally, when carbonyl sulfide is used, only one mole equivalent of halide, or 33-50% that produced using phosgene, is produced thereby having less disposal problem. In this process, however, the hydrocarbyl chloride is added to a reaction medium after formation of a thiolcarbamate salt. The solvent and excess secondary amine are recovered after neutralization with an aqueous caustic solution. The weight percent as well as the productivity of the thiolcarbamate in the crude organic phase using this process is generally very low, for example, about 25 weight %.
Therefore, there is an ever-increasing need for an improved process for producing thiolcarbamates. It would also be a significant contribution to the art if a process having an increased product yield, a simplified process, an improved reaction rate, a shortened reaction time, an increased product productivity, or combinations of two or more thereof can be developed. Because of the large market of thiolcarbamates, seemingly small improvements in the process for producing thiolcarbamates often translate into low manufacturing costs and large savings to consumers.